body {
  display: grid;
  grid-template-columns: minmax(150px, 25%) 1fr;
  padding: 0;
  margin: 0;
}

.sidebar {
  height: 100vh;
  
  /* //   etc. */
  background: lightpink;
  font-size: 2rem;
  text-align: center;
}

.content {
  padding: 2rem;
}

.box {
  width: 200px;
  height: 200px;
  background-color: lemonchiffon;
}